South African Arbovirus No. 86 (S.A.AR86) is a synthetic isolate of Sindbis virus. S.A.AR 86 was originally isolated from mosquitoes. The virus is antigenically related to Sindbis virus and to two other arbovirus isolates, Girdwood and Ockelbo82. See, Malherbe et al., South African Medical Journal, 37:547 (1963) and Niklasson et al., Am. J. Trop. Med. Hyg. 33:1212 (1984), respectively. The latter is associated with a human disease, also known as Ockelbo. Sindbis virus is the prototype member of the alphavirus genus of the Togaviridae. The Sindbis virus includes various stains, including S.A.AR86 and Sindbis AR339. The genome of the Sindbis virus is a single strand of RNA which contains the information for the viral genes, and which is infectious when introduced into the cytoplasm of cells.
Full-length cDNA clones of positive-strand RNA viruses are important tools for the study of the biology of viruses including Sindbis viruses. It is known with respect to several viral systems that in vitro transcripts of cDNA clones, and in some cases the cDNA itself, can initiate a complete and productive infectious cycle upon introduction into susceptible cells. See Racaniello et al., Science 214:916 (1981); Ahlquist et al., Proc. Natl. Acad. Sci. USA 81:7066 (1984); Kaplan et al., Proc. Natl. Acad. Sci. USA 82:8424 (1985); Mizutani et al., J. Virol. 56:628 (1985); van der Werf, Proc. Natl. Acad. Sci. USA 83:2330 (1986); Rice et al., J. Virol. 61:3809 (1987); and Vos et al., Virology 165:33 (1988). This has made it possible to test progeny virus for phenotypic manifestations of directed mutations and recombinations which have been introduced into the cDNA clone. Pathogenesis studies with several positive-strand viruses, including the picornaviruses and the alphaviruses have been advanced significantly by the use of full-length cDNA clones.
As another useful application, live attenuated viral vaccines may be produced using full-length cDNA clones. Live attenuated viral vaccines are among the most successful means of controlling viral disease. However for some virus pathogens, immunization with a live virus strain may be either impractical or unsafe. Sindbis virus is subclinical in humans, but is closely related to other viruses which do induce clinical diseases in humans, such as Ockelbo, an epidemic polyarthritis syndrome common in areas of Scandinavia and Northern Europe. Accordingly, Sindbis virus vaccines are desirable for producing an immunogenic response to such clinical diseases. Sindbis virus vaccines are also desirable as viral carriers in virus constructs which express genes encoding immunizing antigens for other viruses. See U.S. Pat. No. 5,217,879 to Huang et al. Huang et al. '879 describes sindbis infectious viral vectors. However, the reference does not describe the cDNA sequence of S.A.AR86 virus, or clones or viral vectors produced therefrom.
Accordingly, there remains a need in the art for full-length cDNA clones of positive-strand RNA viruses, such as the S.A.AR86 strain of Sindbis. In addition, there is a need in the art for full-length cDNA clones of S.A.AR86 encoding infectious RNA transcripts. Further, there remains a need in the art for cDNA clones of S.A.AR86 which encode RNA transcripts which may be used to produce infectious attenuated vital particles, and methods of producing such viral particles.